The next step of the StarTrucc 22 keel construction was the bulb. In the design phase, we decided to perform a short CFD optimization.
To investigate the effect of different geometries on the tip vortex, the bulb and one meter of keel were simulated. The starting point was a revolved symmetrical airfoil, this was compared to the typical oval cross-section with flat tail found on most modern sailing yachts. As the results from the calculations were available, the advantages of this shape were confirmed. We manually made small changes from one CFD run to the next.
The symmetrical revolved bulb has less surface area and therefore less viscous drag, the penalty in pressure drag, however, more than compensates this advantage. The flat tail also acts as a winglet, reducing the tip vortex.
As can be seen from the plots, the pressure distribution was also smoothed. From 1.5 degrees of angle of attack, the optimized shape has a superior lift to drag ratio. With more computational power a true numerical optimization could be performed and radical shapes could be tested. However we were happy with the result and were eager to tackle the build phase.